1. Field of the Invention
The present invention relates to a battery. More particularly, the present invention relates to a pouch type battery and a method of making the same.
2. Description of the Related Art
Batteries may employ any of a number of electrochemical technologies and may be manufactured in a variety of form factors. Generally, batteries may be classified as primary, or single use, and secondary, or rechargeable. Various battery technologies employ lithium, e.g., lithium secondary batteries, and generally use a non-aqueous electrolyte because of the reactivity between lithium and water. This electrolyte may be, e.g., a solid polymer containing lithium salts or a liquid in which lithium salts are dissociated in some type of organic solvent. Lithium secondary batteries include lithium metal and lithium-ion batteries using an organic liquid electrolyte, and lithium ion polymer batteries using a polymer solid electrolyte. In solid type lithium ion polymer batteries, there is little risk of leaking electrolyte, whereas in liquid or gel type lithium ion polymer batteries there is a chance of leaking the organic electrolyte.
For batteries where the risk of leaking electrolyte is low, a pouch may be used as the battery housing, in contrast to the metal can that is typically employed for batteries having a higher risk of leaking electrolyte. When the pouch is used, it is generally possible to reduce the weight and thickness of the battery and to freely change the shape of the battery, in comparison with the case where the metal can is used.
FIG. 1 illustrates a perspective view of a conventional pouch type battery before the pouch is sealed, FIG. 2 illustrates a perspective view of the battery of FIG. 1 after sealing and folding the pouch, and FIG. 3 illustrates a sectional view taken along the line A-A of FIG. 2. Referring to FIGS. 1-3, a conventional pouch type battery may include an electrode assembly 3 and a pouch material 4 accommodating the electrode assembly 3.
Referring to FIG. 1, a method of forming the conventional pouch type battery will now be described. First, the center of the roughly rectangular pouch material 4 may be folded to form a rear portion 4b and a front portion 4a. A recess 6 in which the electrode assembly 3 can be accommodated may be formed in the rear portion 4b. Sealing portions 5 may be used to seal the front and rear portions 4a and 4b together. A core cell formed as just described may be housed in a hard case to form a hard pack battery (not shown). Otherwise, both lengthwise ends may be dosed with a hot melt resin.
When the hard pack is formed using the bare cell without folding the sealing portions 5, the hard case may require additional space to accommodate the sealing portions 5. Therefore, the sealing portions 5 may be folded toward the respective sides of the recess 6, as illustrated in FIG. 2. Even when the pouch is not put in a hard case, the sealing portions 5 of the pouch may be folded to reduce the overall width of the battery.
As illustrated in FIG. 3, the recess 6 in the conventional pouch type battery may have side walls that are essentially straight or angled at close to 90°. Accordingly, when the sealing portions 5 are folded toward the recess 6, the folded sealing portions 5 are also essentially straight or slightly angled. As a result, if combined with the electrode assembly 3 having rounded sides, the interior portion of the conventional pouch type battery would not be efficiently filled. Thus, the electrical capacity of the battery per unit volume is not maximized. In addition, referring to FIG. 3, folding the sealing portions 5 in this manner increases the overall width of the bare cell by an amount 2W, where W is the width of each of the sealing portions 5 along the respective side surfaces of the pouch.
It will be appreciated that the conventional pouch type battery limits the size of the electrode assembly 3 that can be disposed therein, due to the additional 2W width of the pouch case that is occupied by the sealing portions 5. Moreover, if the pouch case is to be disposed in a hard case, during the assembly process the angled edges of the pouch case may contact the hard case, causing damage to the pouch case. Since the pouch may be very thin, the electrode assembly 3 may be easily damaged.
Additionally, the hard case may have a wall thickness of about 0.6 mm, which makes the completed battery thicker. Accordingly, if the device for which the conventional pouch type battery is intended imposes a limitation on the battery size, the electrical capacity of the battery may be reduced. Conversely, increasing the electrical capacity of the battery may require a larger battery, which may require design changes to other aspects of the device to be powered.